Steps:
1) Create a new Unity project
1a) Go to Editor settings, change Serialization Mode to "Force Text"
2) Save the scene, name it anything
3) Create a new C# file, name it "Dummy"
4) Edit Dummy.cs like this:

[System.Serializable]
class Dummy {
public string Foo;
}

5) Create a new C# file, name it "CrashUnity"
6) Edit CrashUnity.cs like this:
class CrashUnity: MonoBehaviour {
public Dummy Base; // NAME IS IMPORTANT
}

7) Create a new gameObject in the scene, name irrelevant
8) Attach CrashUnity.cs to the new gameobject
9) Click on the new gameobject and save the scene.
10) (EXPECTED) Unity does not crash. GameObject shows a "Base" field which allows one to edit "Foo".
10) (OBSERVED) Unity crashes.